Unit 3

• What is a water deficit?


  When an area lacks sufficient water to meet its needs.
• What are the meteorological causes of water deficit?


  • Droughts: extended period of low or absent rainfall.
  • Caused by variations in normal atmospheric pressure systems.
• What happens during low pressure in the atmosphere?


  Air rises and precipitation occurs.
• What happens during high pressure in the atmosphere?


  Air descends and there is no precipitation.
• How does the jet stream affect weather patterns?

  • The position of the polar front depends on the jet stream.
  • The jet stream moves in waves called Rossby Waves.
  • Rossby Waves determine where high and low pressure will occur.
• What was the position of the jet stream during the 1976 UK drought?


  The jet stream was further north than normal.
• What were the consequences of the high pressure over the UK during the 1976 drought?


  It caused high summer temperatures over 32 degrees Celsius and 65% less rain.
• What is a megadrought?


  A multi-decade event with periods of high severity droughts.
• How has climate change affected the megadrought in the Western USA?

  Temperatures have increased by 1.2 degrees Celsius since 2000 on average.
• What are the impacts of the megadrought on reservoirs like Lake Mead?


  It has caused the shrinking of reservoirs.
• What has been the effect of the megadrought on forest fires in the Western USA?

  10 times more area has been burnt than 40 years ago.
• What is the significance of the California Central Valley in the USA?

  • Produces 1/3 of USA fresh food.
  • Increases pressure on aquifers.
• What is the consequence of digging into aquifers in the California Central Valley?


  It causes subsidence and clay compaction, lowering ground level.
• How long would it take for the aquifer in the California Central Valley to refill?

  It would take around 50 years.